A) Field of the Invention
The present invention relates to optical transmission path forming techniques using optical fibers, and more particularly to an optical fiber array, an optical fiber positioning method to be used for manufacture of an optical fiber array, and an optical fiber positioning plate to be used for the optical fiber positioning method.
B) Description of the Related Art
As a centering method for a ferrule (optical fiber holder), the positions of optical fiber holding holes have been determined conventionally by using the outer periphery of an optical fiber holder as a reference position. A multi optical fiber holder adopting such a centering method is known such as shown in FIG. 43 (for example, refer to the Official Gazette JP-A-HEI-11-712644).
A multi optical fiber holder 1 shown in FIG. 43 has a first recess 2 and a second recess 3 in the upper part of the rectangular body of the holder 1. The first recess 2 is formed spaced apart by a predetermined distance from the end face 1A. The second recess 3 is continuous with and deeper than the first recess 2. Optical fiber positioning holes 1a to 1d are formed in line through the body of the holder between the end face 1A and first recess 2. Optical fiber alignment grooves 4a to 4d of a C-character cross section are juxtaposed on the bottom of the recess 2 and reach the recess 3. Each optical fiber alignment groove has a region 5a as shown in the groove 4a near the recess 3, the region 5a increasing its diameter toward the recess 3. On opposite sides of the end face 1A, guide pin holes G1 and G2 are formed along the row of the positioning holes 1a to 1d. 
A multi optical fiber 6 has optical fibers 8a to 8d covered with a sheath 7. When the multi optical fiber 6 is assembled with the multi optical fiber holder 1, part of the sheath 7 is cut to expose the optical fibers 8a to 8d. The optical fibers 8a to 8d are inserted from the recess 3 side of the holder 1 into the positioning holes 1a to 1d via the alignment grooves 4a to 4d to project the ends of the optical fibers 8a to 8d out of the positioning holes 1a to 1d and sit the sheath 7 on the recess 3. In this state, adhesive is flowed in the alignment grooves 4a to 4d to fix the optical fibers 8a to 8d to the positioning holes 1a to 1d. 
According to this prior art, the positions of optical fibers relative to the outer periphery of the optical fiber holder are determined by the positioning holes 1a to 1d. Therefore, the size and position of each positioning hole 1a to 1d are required to have high precision. The pitch of positioning holes of the multi optical fiber holder is also required to have high precision.
A two-dimensional optical fiber array is know such as shown in FIG. 44 (for example, refer to the Official Gazette of JP-A-HEI-10-268145).
In a two-dimensional optical fiber array shown in FIG. 44, holes H1, H2, H3, . . . are formed through a ceramic plate 1a by precision laser work. Such ceramic plates 1b, 1c, . . . are prepared. Guide lines are inserted into a plurality of holes H1, H2, H3, . . . to align hole positions and stack and fix the ceramic plates 1a, 1b, 1c, . . . . After the guide lines are pulled out of the holes, optical fibers 2a, 2b, 2c, . . . are inserted into the holes H1, H2, H3, . . . and fixed. The ends of the optical fibers 2a, 2b, 2c, . . . are made flush by polishing an end face of the ceramic plate lamination.
According to this prior art, a plurality of optical fibers can be disposed two-dimensionally at high precision. However, position alignment of a number of holes between a plurality of ceramic plates is not easy even if a precision work is performed, and in addition it is not easy to insert optical fibers through a number of holes in the ceramic plate lamination.